The present invention relates generally to the field of fibers. More particularly, the present invention relates to a process for producing yarn having reduced heatset shrinkage.
Polyamide, particularly nylon 6, has been used extensively as a synthetic fiber. Its structural and mechanical properties make it attractive for use in such capacities as face fiber for carpeting.
Polyamide fibers, yarns, carpets, and fabrics are often heatset using either moist or dry heat to provide the fibers, yarns, carpets, and fabrics with dimensional stability. A steaming unit made by Superba of Mulhouse, France or American Superba, Inc. of Charlotte, N.C. is typical of the equipment employed in heatsetting with moist heat. Typically, the heatsetting temperature for nylon 6 is in the range of 124xc2x0 C. to 127xc2x0 C. Polyamide fibers, yarns, carpets, and fabrics often shrink during heatsetting. The typical heatset shrinkage encountered with 100 percent nylon 6 fibers, etc. is about 24 percent to about 32 percent. High heatset shrinkage can hurt carpet wear performance and appearance; therefore, less heatset shrinkage is desirable. One way of obtaining less shrinkage is to heatset nylon 6 fibers, yarns, carpets, and fabrics at a lower temperature. Heatsetting at a lower temperature is advantageous because it provides an environment that is not as harsh and results in a savings of both energy and energy costs. Commonly, however, lower heatset temperatures are undesirable because the resulting carpet product lacks the characteristics of acceptable appearance and wear performance required by the marketplace. For example, the resulting carpet product sometimes shows streaks and chevrons when dyed and may lack properties such as good tip definition and good cover.
It is, therefore, an object of the present invention to reduce the heatset shrinkage that results during the production of fibers, yarns, carpets, and fabrics.
Another object of the present invention is to reduce the temperature at which fibers, yarns, carpets, and fabrics are heatset while still obtaining a desirable end product.
Thus, according to the present invention, there is provided a process for producing yarn having reduced heatset shrinkage comprising the steps of texturing a yarn of bicomponent fibers having a nylon 6 sheath and a core of a fiber-forming polyolefin selected from the group consisting of polypropylene and copolymers thereof to a spinnerette and applying steam at a temperature to the yarn of bicomponent fibers using a steaming unit, wherein the heatset shrinkage of the yarn of bicomponent fibers is about one third to about one half of the heatset shrinkage of a yarn formed of 100 percent nylon 6 fibers and having steam applied thereto at said temperature.
Most preferably, the bicomponent fibers are concentric sheath/core structures having a polyamide sheath and a polyolefin core, wherein the sheath comprises from about 70 percent by weight to about 85 percent by weight of the fibers. Such bicomponent fibers exhibit desirable physical properties that are comparable to and even better than fibers formed of 100 percent nylon 6. The polyolefin core may optionally include one or more inert organic fillers so as to affect the total fiber density (compensating for the lower density of the polyolefin core as compared to the polyamide sheath).
The above and other objects, effects, features, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments thereof.
To promote an understanding of the principles of the present invention, descriptions of specific embodiments of the invention follow, and specific language is used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is intended by the use of this specific language and that alterations, modifications, equivalents, and further applications of the principles of the invention discussed are contemplated as would normally occur to one of ordinary skill in the art to which the invention pertains.
As used herein, the term xe2x80x9cfiberxe2x80x9d includes fibers of extreme or indefinite length (i.e., filaments) and fibers of short length (i.e., staple fibers). The term xe2x80x9cyarnxe2x80x9d refers to a continuous strand or bundle of fibers.
As used herein, the term xe2x80x9cbicomponent fiberxe2x80x9d refers to a fiber having at least two distinct cross-sectional domains respectively formed of from two or more polymer types. The term xe2x80x9cbicomponent fiberxe2x80x9d is, therefore, intended to include concentric and eccentric sheath/core fiber structures, symmetric and asymmetric side-by-side fiber structures, island-in-sea fiber structures, and pie wedge fiber structures. Preferred fiber structures according to the present invention are bicomponent sheath/core fiber structures having a nylon 6 sheath and a core comprised of polypropylene or copolymers thereof. While the following disclosure will be directed to such a preferred embodiment, the present invention is equally applicable to other bicomponent fiber structures having a polyamide domain and a polyolefin domain.
As used herein, the term xe2x80x9ccoverxe2x80x9d refers to the degree to which the underlying structure is concealed by the surface material. With respect to carpets, cover is the degree to which pile covers the backing. A lack of cover means that, upon visual examination, the backing can be seen.
Broadly, the present invention is a process for producing yarn having reduced heatset shrinkage comprising the steps of texturing a yarn of bicomponent fibers having a nylon 6 sheath and a core of a fiber-forming polyolefin selected from the group consisting of polypropylene and copolymers thereof and applying steam at a temperature to the yarn of bicomponent fibers using a steaming unit, wherein the heatset shrinkage of the yarn of bicomponent fibers is about one third to about one half of the heatset shrinkage of a yarn formed of 100 percent nylon 6 fibers and having steam applied thereto at said temperature.
The polyamides useful to form the sheath of the sheath/core bicomponent fibers of the present invention are those long chain synthetic polymers containing amide (xe2x80x94COxe2x80x94NHxe2x80x94) linkages along the main polymer chain that are generically known as nylon 6. Suitable polyamides can also be copolymers of nylon 6, as well as other polyamides having heatset shrinkage properties similar to nylon 6 and copolymers thereof.
Importantly, the core of the fibers according to this invention comprises a fiber-forming polyolefin. Preferred polyolefins are polypropylene and copolymers thereof.
Preferably, the sheath comprises from about 70 percent by weight to about 85 percent by weight of the fibers, while the core comprises from about 15 percent by weight to about 30 percent by weight of the fibers. More preferably, the sheath comprises from about 74 percent by weight to about 79 percent by weight of the fibers, and the core comprises from about 21 percent by weight to about 26 percent by weight of the fibers. Weight ratios of the sheath to the core in the fibers may range from about 2.3:1 to about 10:1. A ratio greater than about 3:1 is particularly preferred.
The core may optionally include an inert organic particulate filler material dispersed therein. The filler material must have an average particle size that is sufficiently small to pass through the polymer filter of the spinnerette without affecting filter pressure. In this regard, particulate filler materials having a particle size in the range between about 0.05 xcexcm and 1.00 xcexcm, and preferably less than about 0.50 xcexcmm, may be employed. When used, the filler material may be blended in a melt of the polyolefin core resin prior to the co-melt spinning of the polyolefin core resin and the polyamide sheath resin using conventional melt-blending equipment. For example, the filler material may be introduced via a side arm associated with an extruder that melts the polyolefin and blends the introduced filler material therein upstream of the spinnerette pack.
Suitable particulate filler materials include calcium carbonate, alumina trihydrate, barium sulfate, calcium sulfate, mica, graphite, kaolin, silica, talc, and titanium dioxide. Calcium carbonate is particularly preferred.
The sheath/core fibers may be spun using conventional fiber-forming equipment. For example, separate melt flows of the sheath and core polymers may be fed to a conventional sheath/core spinnerette pack such as those described in U.S. Pat. No. 5,162,074 to Hills, U.S. Pat. No. 5,125,818 to Yeh, U.S. Pat. No. 5,344,297 to Hills, and U.S. Pat. No. 5,445,884 to Hoyt et al., the entire content of each patent being expressly incorporated hereinto by reference. The melt flows are combined in the spinnerette pack to form extruded fibers such as, for example, multi-lobal (e.g., trilobal, tetralobal, pentalobal, or hexalobal), pentagonal, square, etc. fibers, having sheath/core configurations. Preferably, the fibers have a trilobal structure with a modification ratio of at least about 1.4. More preferably, the modification ratio is about 2 to about 4. In this regard, the term xe2x80x9cmodification ratioxe2x80x9d means the ratio R1/R2, where R2 is the radius of the largest circle that is wholly within a transverse cross-section of the fiber and R1 is the radius of the circle that circumscribes the transverse cross-section.
Conventional steps, such as those known to ones of ordinary skill in the art, may be employed following spinning. For example, the extruded fibers may be quenched, for example with air, in order to solidify the fibers. The fibers may then be treated with a finish comprising a lubricating oil or a mixture of oils and antistatic agents.
Subsequently, the yarn may be drawn and textured to form a bulked continuous filament (xe2x80x9cBCFxe2x80x9d) yarn. A preferred technique involves combining the extruded or as-spun fibers into a yarn and then drawing, texturing, interlacing, and winding the yarn into a package all in a single step, i.e., without intermediate winding after spinning. This one-step method of making BCF yarn is generally known in the art as spin-draw-texturing (SDT). A two-step method wherein the extruded or as-spun fibers are first combined to form a yarn bundle that is wound on a suitable package and are later drawn, textured, and interlaced, and then wound a second time in a separate step may also be used.
The BCF yarns can subsequently go through various processing steps well known to those skilled in the art. For example, the yarn may be twisted into a cabled yarn (xe2x80x9ccable-twistedxe2x80x9d). After the yarn is cable-twisted, the yarn is heatset (xe2x80x9ctwistsetxe2x80x9d) by applying steam to the yarn using a steaming unit. In a preferred method of heatsetting the yarn, the steaming unit comprises a steam tunnel with a prebulker manufactured by Superba of Mulhouse, France or American Superba, Inc. of Charlotte, N.C. The yarn first passes into the prebulker, which is operating at a temperature between about 88xc2x0 C. and about 98xc2x0 C. The yarn then passes from the prebulker into a cooling chamber and into the steam tunnel where steam is applied to the yarn. The temperature of the steam tunnel is between about 116xc2x0 C. and about 127xc2x0 C., preferably between about 118xc2x0 C. and about 123xc2x0 C.
Yarns formed according to the present invention, both at typical nylon 6 heatsetting temperatures (i.e., about 124xc2x0 C. to about 127xc2x0 C.) and at reduced heatsetting temperatures (i.e., about 118xc2x0 C. to about 123xc2x0 C.) exhibit desirable properties, particularly reduced heatset shrinkage, as compared to yarns formed from 100 percent nylon 6 fibers processed at the same heatset conditions. The heatset shrinkage of yarns formed according to this invention is between about 10 percent and 15 percent, preferably between about 11 percent and 14 percent. The heatset shrinkage of yarns formed according to this invention, therefore, is reduced to about one third to one half of the heatset shrinkage of yarns formed from 100 percent nylon 6 fibers.
Carpet may be made from the yarn by conventional carpet-making techniques such as weaving or tufting the fibers into a backing material and binding the fibers to the backing with latex or other adhesives. The carpet may be cut-pile, berber, unlevel loop, level loop, or any other style according to the popular fashion. If desired, the carpet may be in the form of carpet tiles, with or without foam backing. By way of example, in the case of cut-pile carpeting, the yarn is tufted into a primary backing and cut to form cut-pile carpeting. The primary backing material may be woven or nonwoven jute, nylon, polyester, polypropylene, etc. The cut-pile carpeting is dyed to the desired shade. The primary backing is then coated with a suitable latex material such as a conventional styrene-butadiene (xe2x80x9cSBxe2x80x9d) latex, vinylidene chloride polymer, or vinyl chloride-vinylidene chloride copolymers. It is common practice to use fillers such as calcium carbonate to reduce latex costs. The final step is to apply a secondary carpet backing to the latex-based adhesive. The secondary backing may be jute, polypropylene, nylon, polyester, etc. The carpet may be foam backed or not. The carpet of the present invention can be a variety of pile weights, pile heights, and styles. There is not currently believed to be any limitation on the carpet style.
Surprisingly, carpets formed from the bicomponent yarns made according to the present invention at reduced heatsetting temperatures have the characteristics of acceptable appearance and wear performance required by the marketplace. Unlike carpets formed from yarns made of 100 percent nylon 6 fibers when heatset at reduced heatsetting temperatures, the carpets formed from the bicomponent yarns made according to the present invention at reduced heatsetting temperatures have a uniform appearance with good tip definition and good cover. When dyed, the carpets formed from the bicomponent yarns heatset according to the present invention at reduced heatsetting temperatures also lack the streaks and chevrons found in the carpets made from yarns of 100 percent nylon 6 fibers when those are heatset at the same reduced heatsetting temperatures.
While the discussion above has emphasized the fibers made according to the present invention being formed into bulked continuous filaments for the purpose of making carpet fibers, the fibers may also be processed to form fibers for a variety of textile applications such as, for example, fabrics. In this regard, the fibers may be crimped or otherwise textured and then chopped to form random lengths of staple fibers having individual fiber lengths varying from about 1.5 to about 8.0 inches.
Additionally, the fibers may be dyed or colored utilizing conventional fiber-coloring techniques. For example, the fibers of this invention may be subjected to an acid dye bath to achieve desired fiber coloration. Alternatively, the nylon sheath may be colored in the melt prior to fiber formation (i.e., solution dyed) using conventional pigments for such purpose.
The invention will be further described by reference to the following detailed examples. The examples are set forth by way of illustration and are not intended to limit the scope of the invention.
Physical properties for the samples in the Examples below were obtained using the following test procedures:
Linear Density
The linear density of the fibers was determined using ASTM D1907, where the length of the yarn used was 90 cm.
Superba Shrinkage
Percent shrinkage was computed using the linear densities before and after Superba heatsetting of the yarn by the formula:       Percent    ⁢          xe2x80x83        ⁢    shrinkage    =                    "LeftBracketingBar"                  (                                    d              after                        -                          d              before                                )                "RightBracketingBar"                    d        after              xc3x97    100  
where dbefore and dafter are respectively the linear densities before and after the Superba heatsetting.
Dry Bulk Development
This test measures skein bulk development of steam bulked carpet yarns that are exposed to dry heat under a light load. Each yarn sample (i.e., 100 percent nylon 6 and the bicomponent yarn) is wound in the form of a skein, and a load of 14 grams (xe2x80x9clight loadxe2x80x9d) is attached to the skein. The skein with the light load is exposed to dry heat at a temperature of 149xc2x13xc2x0 C. for 5 minutes. After 5 minutes of heating, the inside loop length of the skein with the light load attached is immediately measured to the nearest millimeter. An additional 1350-gram load is then placed on the skein (for a total of 1364 grams). After 30xc2x13 seconds, the inside loop of the skein is measured to the nearest millimeter (L2).
Percent dry bulk development is determined using the following equation:       Percent    ⁢          xe2x80x83        ⁢    dry    ⁢          xe2x80x83        ⁢    bulk    =                              L          2                -                  L          1`                            L        2              xc3x97    100  
where L1 is skein loop length with the 14-gram load in centimeters and L2 is skein loop length with the 1364-gram load in centimeters.
Wet Bulk Development
This test measures skein bulk development of steam bulked carpet yarns that are subjected to hot water under a light load. Each yarn sample (i.e., 100 percent nylon 6 and the bicomponent yarn) is wound in the form of a skein, and a tensioning weight equivalent to 0.056 gf/den (0.5 gf/tex) is attached to the skein. The inside loop length of the skein is measured to the nearest millimeter (Lo) about 30xc2x13 seconds after attaching the weight to the skein. The tensioning weight is then removed, and a 4.5-gram weight is attached to the skein. The skein with the attached weight is then immersed in a hot water bath for 30 seconds. After 30 seconds, the inside loop length of the skein with the weight attached is measured to the nearest millimeter (Lf).
Percent wet bulk development is determined using the following equation:       Percent    ⁢          xe2x80x83        ⁢    wet    ⁢          xe2x80x83        ⁢    bulk    =                              L          o                -                  L          f                            L                  2          ⁢          o                      xc3x97    100  
where Lo is the original loop length of the skein in centimeters and Lf is the final loop length of the skein after wet treatment in centimeters.
Boiling Water Shrinkage
This procedure, which incorporates the principles of ASTM D2259-71, measures the shrinkage of yarn in skein form when exposed to boiling water. The shrinkage of yarn in skein form is defined as the change in loop length of a skein expressed as a percentage of the length prior to exposure to the boiling water.
In this procedure, each yarn sample (i.e., 100 percent nylon 6 and the bicomponent yarn) is wound in the form of a skein, and a tensioning weight is attached to the skein. After 30xc2x13 seconds, the inside loop of the skein is measured to the nearest millimeter (Lo). The skein is then immersed in a bath of boiling water for 30 minutes. After 30 minutes, the skein is removed and dried. A tensioning weight is then attached to the skein. After 30xc2x13 seconds, the inside loop of the skein is measured to the nearest millimeter (Lf).
Percent boiling water shrinkage is determined using the following equation:       Percent    ⁢          xe2x80x83        ⁢    shrinkage    =                              L          o                -                  L          f                            L        o              xc3x97    100  
where Lo is the original loop length of the skein and Lf is the final loop length of the skein after treatment.
Elongation and Tenacity
The elongation and tenacity of the yarn were determined using ASTM D2256-97.
Modulus at 5 Percent Extension
The modulus at 5 percent extension was determined using ASTM D2256-97.